For Marco Rubio, his contrast with Hillary Rodham Clinton is generational. She’s so yesterday, the youthful Florida senator says, while I’m a leader for the future.

Wisconsin Gov. Scott Walker roots his comparison with the Democratic presidential front-runner in class and background, arguing that he is an everyman outsider and that Clinton is a lifelong Washington insider.

And Jeb Bush sees a winning pitch in holding up his concrete accomplishments as Florida governor against Clinton’s less tangible record and casting himself as accessible and her as secretive.

Clinton’s official entrance into the 2016 presidential race and her dominance in early polls has crystallized the challenge for the nearly two dozen Republicans hoping to take her on: How to beat her?

The contenders and their advisers agree on an overarching objective — to portray Clinton as a tired throwback to an earlier era, a liberal artifact who has been around too long, whose ideas are outdated and whose political baggage is heavy.

“Whatever you associate with Hillary Clinton, whether it’s Bill Clinton or Barack Obama, it’s the past,” said Sean Spicer, the Republican National Committee’s chief strategist. “That’s where we see an opening to talk about the future in a convincing way.”

But the narratives that the Republicans are beginning to tell about Clinton are also divergent — in message and emphasis, in biography and presentation — forcing the party to pick just one course from a menu of possibilities. Across the GOP, from campaign masterminds to grass-roots activists, there is growing debate about which candidate could be Clinton’s sharpest foil.

“Some guys will take a sledgehammer towards her; others will use a stiletto,” said David Carney, a veteran Republican consultant. “There will be lots of strategies in the back alleys as they figure out how to do it.”

Republicans’ near-uniformity on key issues has intensified the competition to be viewed as the one best poised to beat Clinton, in which their personal backgrounds and political presentations are important differentiating factors.

Republicans also feel an urgency to start defining Clinton in a negative light before her candidacy is fully formed. Clinton is only now reemerging from a political winter since her 2008 campaign.

Her GOP foes have amped up their rhetoric; this month in New Hampshire, they tested one attack line after another. Sen. Rand Paul (R-Ky.), who has been perhaps the most combative anti-Clinton voice, quipped that she would need two campaign planes — “one for her and her entourage and one for her baggage.”

Hillary Rodham Clinton greets June Whitcomb and other voters at an April campaign event in Concord, N.H. (Melina Mara/The Washington Post)

Clinton has noticed. “The Republicans seem to be talking only about me,” she recently said with a smile. “I don’t know what they’d talk about if I wasn’t in the race.”

Virginia Gov. Terry McAuliffe (D) argues that the GOP’s Clinton fixation will hurt them. “If they spend all their time attacking Hillary, it’s great news for us,” he said. “Let her lay her agenda out there. I can’t tell you today where one Republican stands on an issue, but I know the little joke lines they use on Hillary. That is a missed opportunity for them.”

In subtle ways, each GOP hopeful is trying to use his or her own attributes to build a unique case against Clinton.

Rubio (R-Fla.) has presented the most vivid contrast, making his generational differences with Clinton a centerpiece of his nascent campaign. Announcing his candidacy in Miami this month alongside his wife and four children, he defined the coming election as “a generational choice about the kind of country we will be.”

Rubio — who at 43 is young enough to be Clinton’s son — called the 67-year-old Democrat “a leader from yesterday . . . promising to take us back to yesterday.” He talks casually about his affinity for football and rap music (he counts the rapper Pitbull as a friend), signaling to young people that he is not their father’s country-club Republican.

Walker (R-Wis.) is emphasizing his Midwestern, devoutly Christian upbringing and relatable suburban lifestyle. He often mentions his coupon-aided purchases at Kohl’s and Jos. A. Bank and his hobby of riding Harley-Davidson motorcycles. On the stump, Walker, 47, derides Clinton as a fixture of the East Coast political elite. “I doubt the presumptive nominee for the other party has ever been to Kohl’s,” Walker joked this month.

Some conservatives say the easiest approach is to go back to the well by questioning the character of Clinton and her husband.

“Character is everything and gets at the deeper reservations out there,” said R. Emmett Tyrrell Jr., editor of the American Spectator, a conservative monthly magazine that has long clashed with the Clintons. “Rand Paul is making a proper issue of it — and Jeb Bush should, too. Remind people about the dignity his family has shown in the White House.”

Polling suggests character is a potential vulnerability. A Quinnipiac University survey of registered voters last week found that 54 percent do not view Hillary Clinton as honest or trustworthy — though a larger majority, 62 percent, said she has strong leadership qualities.

There are other contrasts, too. Sen. Ted Cruz (R-Tex.) is making ideological overtures, portraying Clinton as a paragon of liberal orthodoxy dating to Lyndon B. Johnson’s War on Poverty and pledging to scale back social programs and eviscerate the federal bureaucracy.

Former Arkansas governor Mike Huckabee is playing up his personal and political past with the Clintons. He recently boasted that he was the only Republican contender who has run against “the Clinton political machine” and defeated it by being elected that state’s governor in 1998 — a point he plans to underscore by launching his campaign May 5 from Hope, Ark., the birth place to both him and Bill Clinton.

“Who can effectively attack Hillary Clinton without coming across as a jerk?” asked Hogan Gidley, a Huckabee adviser. “Mike Huckabee has that ability; he has that winsomeness.”

Further afield is a galaxy of conservative stars who are attacking Clinton to generate attention for their long-shot bids. Businesswoman Carly Fiorina has won notice for brashly belittling Clinton’s tenure as secretary of state.

For Bush , the contrast with Clinton is less visceral. Both are personally wealthy, heirs to political dynasties and favorites of their respective party establishments. So Bush is trying to portray Clinton as an imperial politician with a thin governing record. His advisers say he hopes to undercut Clinton’s argument that she has the know-how to make Washington work better by showing that he had more palpable achievements as governor.

Bush also plans to field questions from voters and reporters at every turn, hoping that his openness will draw attention to Clinton’s more tightly controlled manner. He indicated this approach with one of the first moves of his presidential exploration.

“Jeb started it in December when he announced he was going to release his e-mails,” said Scott Reed, a longtime GOP operative. “That was the first strategic move to hot-box Hillary.”

One challenge for Republicans is that Clinton is a tougher target than she was in her polarizing early years on the national stage. As first lady in the 1990s, she was a partisan warrior, leading an unsuccessful fight for universal health care and sparring with the “vast right-wing conspiracy,” as she put it. But following a tour as secretary of state that softened those edges, she is campaigning as a worldly and wise grandmother.

Another hurdle is the historic nature of Clinton’s candidacy. Her bid to become the first female president is likely to stir enthusiasm among female voters in particular. Republicans are struggling to criticize Clinton’s qualifications without seeming to dismiss the potential of a woman in the Oval Office.

Republican pollster Kellyanne Conway, who has been conducting focus groups of independent women in swing states, said there is a “gender tug.” The imperative, she said, is to separate Clinton from her possible place in the history books.

“ ‘Intelligent,’ ‘strong,’ ‘thoughtful,’ ‘confident’ — that’s what you hear from a fair number of ticket-splitting women,” Conway said. “But then you also hear, ‘calculating,’ ‘conniving,’ ‘yesterday’s news’. Republicans need to ask not, ‘Do you want a woman to be president?’ but, ‘Do you want that woman?’ ”

The distinctions among Republicans reflect the roiling intraparty debate about how best to build a winning coalition after two straight presidential election losses and about who could lead it. In past cycles, Republicans have turned to their eminences — George H.W. Bush in 1988, Bob Dole in 1996, John McCain in 2008 — but this time, there is no candidate who could claim to be the next in line.

“Whenever you have elections about generational change, it’s frequently been the Democrats doing so — an older Republican versus a younger Democrat,” former Mississippi governor Haley Barbour said.

Consider 1992, when Bill Clinton, a 46-year-old baby boomer with a common touch, swept the first President Bush out of the White House. In “The War Room,” a documentary chronicling Clinton’s campaign, adviser James Carville sneered of Bush: “He reeks of yesterday. He has the stench of yesterday. He is so yesterday, if I think of yesterday, if I think of an old calendar, I think of George Bush’s face on it.”

Now, as Bill Clinton’s wife tries to return to the White House, the parties’ roles are reversed.

“We have a huge field, and it’s all about the future,” said Reed, the Republican strategist. “Whoever can capture that is well on their way to being the nominee.”